1. Field of the Invention
The present invention relates to a rotor shaft provided with a bearing positioning portion and an AC generator for vehicle.
2. Background Art
An AC generator in the related art that is attached to an automobile engine and driven by this engine has, as is disclosed in Patent Document 1, a housing of a structure in which a pair of bowl-like front (drive end) frame and rear (rear end) frame is joined together with the respective openings facing each other and a stator in between. At the center, the front frame and the rear frame are provided, respectively, with cylindrical front bearing box (front box) and rear bearing box (rear box) mutually protruding inward in the axial direction. A front bearing and a rear bearing are installed to the front box and the rear box, respectively. Also, a rotation shaft (rotor shaft) of a rotor provided inside the stator is supported on the front bearing and the rear bearing in a rotatable manner. This rotor shaft is driven by an engine via a pulley installed at the tip end protruding outside from the front frame.
The outer ring of the front bearing is fixed to the front bearing box whereas the rear bearing is press-fit to the shaft first and then press-fit to a rear bearing holder and held by the rear box. By providing the rotor shaft with a step about as thick as the bearing inner ring in the radial direction for the bearing to abut thereon, the press-fit position of the rear bearing in the axial direction is determined (see, for example, Document 1).
As a method of maintaining the bearing position, there has been proposed a method of using a bearing retainer plate after the rear bearing is press-fit in the rear bearing box (see, for example, Document 2).
As another example, there has been proposed a bearing fixing device formed of a step surface provided to the main shaft and an annular collar fit in an annular groove formed to be spaced apart from this step by a predetermined distance in the axial direction (see, for example, Document 3).
Patent Document 1: Japanese Patent No. 4306476
Patent Document 2: EP Patent No. 0723087
Patent Document 3: JP-A-2006-125432
The rotor shaft is formed by subjecting a blank shaft to machining operations, such as outside diameter lathe turning, processing, rolling, grinding, and grooving. The rear bearing is press-fit to the shaft by a press machine while being controlled by a press-fit height and a press-fit load. Further, the rotor ASSY (assembly) in which the rear bearing is press-fit is assembled by press-fitting the rear bearing portion of the rear ASSY in the bearing box.
When the bearing portion is press-fit in the bearing box in this manner, in a case where a bearing positioning mechanism is not provided to the rotor shaft, there is a problem that the fitting position of the bearing inner diameter portion shifts in the axial direction. With the shaft in the related art described in Patent Document 1, it is possible to use the step for positioning at the time of bearing press-fit. However, because it is necessary to increase the diameter of the blank shaft, there is a considerable amount of machining margin in LA (lathe turning), rolling, and grooving and the cost is increased. In addition, because the finishing diameter of the shaft becomes larger, the diameter of a slip ring becomes larger, too. This poses problems, such as an increase of the direct material cost and an increase in weight.
The mechanisms in the related art described in Patent Documents 2 and 3 use a plate and screws as a bearing retainer. Hence, there are problems that the number of components is increased and so are the number of assembly man-hours and the material cost.